[clang][CodeComplete] skip explicit obj param in SignatureHelp

clang-tools-extra/clangd/unittests/CodeCompleteTests.cpp

@@ -3266,6 +3266,47 @@ TEST(SignatureHelpTest, VariadicType) {
   }
 }
 
+TEST(SignatureHelpTest, SkipExplicitObjectParameter) {
+  Annotations Code(R"cpp(
+    struct A {
+      void foo(this auto&& self, int arg); 
+      void bar(this A self, int arg);
+    };
+    int main() {
+      A a {};
+      a.foo($c1^);
+      (&A::bar)($c2^);
+      // TODO: (&A::foo)(^c3)
+    }
+  )cpp");
+
+  auto TU = TestTU::withCode(Code.code());
+  TU.ExtraArgs = {"-std=c++23"};
+
+  MockFS FS;
+  auto Inputs = TU.inputs(FS);
+
+  auto Preamble = TU.preamble();
+  ASSERT_TRUE(Preamble);
+
+  {
+    const auto Result = signatureHelp(testPath(TU.Filename), Code.point("c1"),
+                                      *Preamble, Inputs, MarkupKind::PlainText);
+
+    EXPECT_EQ(1, Result.signatures.size());
+
+    EXPECT_THAT(Result.signatures[0], AllOf(sig("foo([[int arg]]) -> void")));
+  }
+  {
+    const auto Result = signatureHelp(testPath(TU.Filename), Code.point("c2"),
+                                      *Preamble, Inputs, MarkupKind::PlainText);
+
+    EXPECT_EQ(1, Result.signatures.size());
+
+    EXPECT_THAT(Result.signatures[0], AllOf(sig("([[A]], [[int]]) -> void")));
+  }
+}
+
 TEST(CompletionTest, IncludedCompletionKinds) {
   Annotations Test(R"cpp(#include "^)cpp");
   auto TU = TestTU::withCode(Test.code());
@@ -4368,11 +4409,14 @@ TEST(CompletionTest, SkipExplicitObjectParameter) {
   Annotations Code(R"cpp(
     struct A {
       void foo(this auto&& self, int arg); 
+      void bar(this A self, int arg);
     };
 
     int main() {
       A a {};
-      a.^
+      a.$c1^s
+      (&A::ba$c2^;
+      // TODO: (&A::fo$c3^
     }
   )cpp");
 
@@ -4386,12 +4430,24 @@ TEST(CompletionTest, SkipExplicitObjectParameter) {
 
   MockFS FS;
   auto Inputs = TU.inputs(FS);
-  auto Result = codeComplete(testPath(TU.Filename), Code.point(),
-                             Preamble.get(), Inputs, Opts);
-
-  EXPECT_THAT(Result.Completions,
-              ElementsAre(AllOf(named("foo"), signature("(int arg)"),
-                                snippetSuffix("(${1:int arg})"))));
+  {
+    auto Result = codeComplete(testPath(TU.Filename), Code.point("c1"),
+                               Preamble.get(), Inputs, Opts);
+
+    EXPECT_THAT(Result.Completions,
+                UnorderedElementsAre(AllOf(named("foo"), signature("(int arg)"),
+                                           snippetSuffix("(${1:int arg})")),
+                                     AllOf(named("bar"), signature("(int arg)"),
+                                           snippetSuffix("(${1:int arg})"))));
+  }
+  {
+    auto Result = codeComplete(testPath(TU.Filename), Code.point("c2"),
+                               Preamble.get(), Inputs, Opts);
+    // TODO: snippet suffix is empty for c2
+    EXPECT_THAT(Result.Completions,
+                ElementsAre(AllOf(named("bar"), signature("(int arg)"),
+                                  snippetSuffix(""))));
+  }
 }
 } // namespace
 } // namespace clangd

clang/lib/Sema/SemaCodeComplete.cpp

@@ -4034,6 +4034,14 @@ static void AddOverloadParameterChunks(
       return;
     }
 
+    // C++23 introduces an explicit object parameter, a.k.a. "deducing this"
+    // Skip it for autocomplete and treat the next parameter as the first
+    // parameter
+    if (Function && FirstParameter &&
+        Function->getParamDecl(P)->isExplicitObjectParameter()) {
+      continue;
+    }
+
     if (FirstParameter)
       FirstParameter = false;
     else

clang/test/CodeCompletion/skip-explicit-object-parameter.cpp

@@ -1,14 +1,42 @@
 struct A {
-  void foo(this A self, int arg);
+  void foo(this auto&& self, int arg);
+  void bar(this A self, int arg);
 };
 
-int main() {
+int func1() {
   A a {};
   a.
 }
-// RUN: %clang_cc1 -cc1 -fsyntax-only -code-completion-at=%s:%(line-2):5 -std=c++23 %s | FileCheck %s
-// CHECK: COMPLETION: A : A::
-// CHECK-NEXT: COMPLETION: foo : [#void#]foo(<#int arg#>)
-// CHECK-NEXT: COMPLETION: operator= : [#A &#]operator=(<#const A &#>)
-// CHECK-NEXT: COMPLETION: operator= : [#A &#]operator=(<#A &&#>)
-// CHECK-NEXT: COMPLETION: ~A : [#void#]~A()
+// RUN: %clang_cc1 -fsyntax-only -code-completion-at=%s:%(line-2):5 -std=c++23 %s | FileCheck -check-prefix=CHECK-CC1 %s
+// CHECK-CC1: COMPLETION: A : A::
+// CHECK-NEXT-CC1: COMPLETION: bar : [#void#]bar(<#int arg#>)
+// CHECK-NEXT-CC1: COMPLETION: foo : [#void#]foo(<#int arg#>)
+// CHECK-NEXT-CC1: COMPLETION: operator= : [#A &#]operator=(<#const A &#>)
+// CHECK-NEXT-CC1: COMPLETION: operator= : [#A &#]operator=(<#A &&#>)
+// CHECK-NEXT-CC1: COMPLETION: ~A : [#void#]~A()
+
+struct B {
+  template <typename T>
+  void foo(this T&& self, int arg);
+};
+
+int func2() {
+  B b {};
+  b.foo();
+}
+// RUN: %clang_cc1 -fsyntax-only -code-completion-at=%s:%(line-2):9 -std=c++23 %s | FileCheck -check-prefix=CHECK-CC2 %s
+// CHECK-CC2: OVERLOAD: [#void#]foo(int arg)
+
+int func3() {
+  // TODO: (&A::foo)
+  (&A::bar)
+}
+// RUN: %clang_cc1 -fsyntax-only -code-completion-at=%s:%(line-2):10 -std=c++23 %s | FileCheck -check-prefix=CHECK-CC3 %s
+// CHECK-CC3: COMPLETION: bar : [#void#]bar(<#int arg#>)
+
+int func4() {
+  // TODO: (&A::foo)(
+  (&A::bar)(
+}
+// RUN: %clang_cc1 -fsyntax-only -code-completion-at=%s:%(line-2):13 -std=c++23 %s | FileCheck -check-prefix=CHECK-CC4 %s
+// CHECK-CC4: OVERLOAD: [#void#](<#A#>, int)